This study aims to establish synchrony as an individual-specific mechanism of therapeutic change and offers novel insights into the mechanisms of curative interpersonal processes. The study identifies individual-specific trait-like synchrony signature and investigates the associations between synchrony signature, the individual's trait-like characteristics, and mental health, among participants diagnosed with Major Depressive Disorder. The study further investigates how deterministic the trait-like synchrony signature is by identifying for whom, how, and when changes are anticipated. Additionally, it examines whether synchrony signature transfers to relationships with the therapist, whether and how it changes throughout treatment, and whether such potential changes are associated with improvements in mental health. Synchrony is recognized as a key driver of collaborative, affiliative, and curative relationships. While its potential role in improving mental health through interpersonal relationships has sparked growing interest, particularly in psychotherapy, the field is at a crossroads, with mixed findings challenging the widespread theoretical assumption that "more synchrony is better." This study introduces a personalized framework that emphasizes individual-specific synchrony signatures, shifting from generalized assumptions to tailored understanding and interventions. The study explores how synchrony can transform relationships into curative ones by leveraging individual-tailored changes in synchrony signatures in psychotherapy. The potential impact is vast. Tailoring synchrony to individual-specific signatures represents a paradigm shift from a one-size-fits-all approach to personalized interventions. This personalized framework could revolutionize mental health care by facilitating the development of targeted strategies that enhance treatment outcomes.

Inclusion Criteria:

• Current major depressive disorder based on the Diagnostic and Statistical Manual of Mental Disorders-5, and scores above 14 on the 17-item Hamilton rating scale for depression at two consecutive assessments, one week apart.
• For participants using psychiatric medication, the dosage must be stable for at least three months before the beginning of the study, and they will be asked to maintain stable dosage during the treatment
• Age between 18 and 65 years
• Hebrew language proficiency
• Provision of written informed consent.

Exclusion Criteria:

• Current risk of suicide or self-harm
• Current substance abuse disorders
• Current or past schizophrenia or psychosis, bipolar disorder, or severe eating disorder requiring medical monitoring
• History of organic mental disease
• Currently in psychotherapy

Data will not be shared due to ethical reasons.